feat(rate-limiting): Implement core rate limiting functionality with configuration, decision-making, metrics, middleware, and service registration

- Add RateLimitConfig for configuration management with YAML binding support.
- Introduce RateLimitDecision to encapsulate the result of rate limit checks.
- Implement RateLimitMetrics for OpenTelemetry metrics tracking.
- Create RateLimitMiddleware for enforcing rate limits on incoming requests.
- Develop RateLimitService to orchestrate instance and environment rate limit checks.
- Add RateLimitServiceCollectionExtensions for dependency injection registration.

src/Cli/StellaOps.Cli/Services/IBackendOperationsClient.cs

@@ -133,4 +133,7 @@ internal interface IBackendOperationsClient
     // CLI-SDK-64-001: SDK update
     Task<SdkUpdateResponse> CheckSdkUpdatesAsync(SdkUpdateRequest request, CancellationToken cancellationToken);
     Task<SdkListResponse> ListInstalledSdksAsync(string? language, string? tenant, CancellationToken cancellationToken);
+
+    // SDIFF-BIN-030: SARIF export
+    Task<string?> GetScanSarifAsync(string scanId, bool includeHardening, bool includeReachability, string? minSeverity, CancellationToken cancellationToken);
 }